1. Field of the Invention
The present invention relates to an optical fiber LED assembly for coupling the light from a light emitting element such as a laser diode (LD) to an optical fiber via a rod lens with distributed refractive index.
2. Description of the Related Art
A problem with an optical fiber LED assembly having the aforesaid structure will be described with reference to FIG. 2 which is a cross-sectional view showing an optical fiber LED assembly which couples the light from a light emitting element to an optical fiber via a rod lens with distributed refractive index.
A light emitter chip 2 is supported in a hermetically sealed space formed by a base 6, a can 3, and a glass pane 5 of a light source element 1. The can 3 of the light source element 1 is inserted in a hole 8b of a first holder 8 and the base 6 is in close contact with and fixed to the hole 8b of the first holder 8.
A rod lens with distributed refractive index 9 is fixed to one end of a second holder 10 and a ferrule 11, which supports an optical fiber 13, is fixed to the other end of the second holder 10.
Both surfaces of the glass pane 5 of the light source element 1 are provided with reflectionless coating for acquiring a reflectance of about 0.2% to about 1% in general. The end surface of the rod lens with distributed refractive index 9 is also provided with similar reflectionless coating.
The light emitting point of the light emitter chip 2, which is the light emitting element, of the light source element 1 does not always coincide with the center of the can 3 surrounding the chip 2. For this reason, if the outer periphery of the can 3 is established as the reference, deviation of the optical axis would take place. To avoid such deviation of the optical axis, it is necessary to accomplish axial alignment of the order of a micron between the structure supporting the light source element 1 and the structure supporting the rod lens with distributed refractive index 9. This need makes it difficult to maintain the airtightness of the structure of the aforesaid apparatus.
Housing the above-mentioned optical fiber LED assembly itself in a vacuum vessel and exhausting air from it adds to the manufacturing cost and it also adds to the size of the entire apparatus, presenting a problem in use.